|Publication number||US7437299 B2|
|Application number||US 10/510,219|
|Publication date||Oct 14, 2008|
|Filing date||Mar 20, 2003|
|Priority date||Apr 10, 2002|
|Also published as||CN1647154A, CN100508026C, EP1500085A1, EP1500085B1, US20050141721, WO2003085643A1|
|Publication number||10510219, 510219, PCT/2003/1152, PCT/IB/2003/001152, PCT/IB/2003/01152, PCT/IB/3/001152, PCT/IB/3/01152, PCT/IB2003/001152, PCT/IB2003/01152, PCT/IB2003001152, PCT/IB200301152, PCT/IB3/001152, PCT/IB3/01152, PCT/IB3001152, PCT/IB301152, US 7437299 B2, US 7437299B2, US-B2-7437299, US7437299 B2, US7437299B2|
|Inventors||Ronaldus Maria Aarts, Roy Irwan|
|Original Assignee||Koninklijke Philips Electronics N.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Non-Patent Citations (1), Referenced by (22), Classifications (19), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to coding multichannel signals including a at least a first and a second signal component. More particularly, the invention relates to the coding of multiphonic audio signals, such as stereophonic signals.
Stereophonic audio signals comprise a left (L) and a right (R) signal component which may originate from a stereo signal source, for example from separated microphones. The coding of audio signals aims at reducing the bit rate of a stereophonic signal, e.g. in order to allow an efficient transmission of sound signals via a communications network, such as the Internet, via a modem and analogue telephone lines, mobile communication channels or other a wireless networks, etc., and to store a stereophonic sound signal on a chip card or another storage medium with limited storage capacity.
U.S. Pat. No. 4,589,127 discloses a transmitter for stereophonic signals which generates sum and difference signals of the stereo L and R signals. The sum and difference signals are subsequently used in a modulation scheme resulting in a modulated signal comprising both the sum and difference information.
However, the above prior art method does not address the problem of encoding a stereo signal with an efficient bit-rate utilisation, i.e. with a low bit rate for a given sound quality.
The above and other problems are solved by a method of encoding a multichannel signal including at least a first signal component and a second signal component, the method comprising the steps of
Consequently, by transforming the multichannel signal into a principal signal which includes most of the energy and a residual signal which only includes little signal energy, the multichannel signal may be represented by the principal signal, the transformation parameter, and optionally a small residual signal, thereby improving the coding efficiency for the multichannel signal. Effectively, the multichannel signal may be encoded with a bit rate which is only slightly higher than that of a single channel, e.g. a mono channel. The resulting encoded signal may be stored and/or communicated to a receiver.
When the method further comprises the step of adaptively determining the transformation parameter based on at least the first and second signal components, the optimal transformation parameter may continuously be tracked, thereby ensuring the transformation remains optimal even if the characteristics of the input signal changes, e.g. in the example of an audio signal due to a moving sound source or changes in acoustic properties of the environment.
When the predetermined transformation is a rotation and the transformation parameter corresponds to an angle of rotation, a simple transformation is provided based only on a single parameter, the angle of rotation. By adapting the angle such that the signal components, e.g. the L and R signal components of a stereo signal, are rotated into a principal component signal and a residual signal, an efficient coding is provided while maintaining a high quality signal.
In a preferred embodiment of the invention, the step of representing the multichannel signal at least by the principal signal and the transformation parameter further comprises the step of representing the multichannel signal by the principal signal, the transformation parameter, and the residual signal, thereby further improving the quality of the encoded signal as no signal information is discarded. As the residual signal is small compared to the principal signal, the bit allocation may be traded between those signals. Furthermore, as the bit rate allocation may be varied, a mechanism for graceful degradation is provided, e.g. by adaptively increasing or decreasing the bit rate allowed for the residual signal.
Consequently, in a further preferred embodiment, the step of representing the multichannel signal by the principal signal, the transformation parameter, and the residual signal further comprises the steps of
In another preferred embodiment,
This embodiment of the invention is based on the recognition that for many multichannel signals, e.g. in the case of audio signals for music and speech signals, the residual signal may be estimated as a filtered version of the principal signal. Hence, when determining a set of filter parameters of an adaptive filter which models the residual signal, the filter parameters may be encoded together with the principal signal and the transformation parameter. Consequently, communicating the residual signal is avoided without loosing the information included in that signal, thereby providing an efficient encoding which preserves a high level of quality.
It is an advantage of the invention that it provides an efficient bit-rate utilisation, i.e. a coding scheme which uses a low bit rate for a given sound quality. The coding scheme according to the invention may be used to reduce the bit rate without significantly reducing the sound quality, to maintain the bit rate while improving the sound quality, or a combination of the above.
The invention further relates to a method of decoding multichannel signal information, the method comprising the steps of
The present invention can be implemented in different ways including the methods described above and in the following, arrangements for encoding and decoding multichannel signals, respectively, a data signal, and further product means, each yielding one or more of the benefits and advantages described in connection with the first-mentioned method, and each having one or more preferred embodiments corresponding to the preferred embodiments described in connection with the first-mentioned method and disclosed in the dependant claims.
It is noted that the features of the methods described above and in the following may be implemented in software and carried out in a data processing system or other processing means caused by the execution of computer-executable instructions. The instructions may be program code means loaded in a memory, such as a RAM, from a storage medium or from another computer via a computer network Alternatively, the described features may be implemented by hardwired circuitry instead of software or in combination with software.
The invention further relates to an arrangement for encoding a multichannel signal including at least a first signal component and a second signal component, the arrangement comprising
The invention further relates to an arrangement for decoding multichannel signal information, the arrangement comprising
The above arrangements may be part of any electronic equipment including computers, such as stationary and portable PCs, stationary and portable radio communications equipment and other handheld or portable devices, such as mobile telephones, pagers, audio players, multimedia players, communicators, i.e. electronic organisers, smart phones, personal digital assistants (PDAs), handheld computers, or the like.
The term processing means comprises general- or special-purpose programmable microprocessors, Digital Signal Processors (DSP), Application Specific Integrated Circuits (ASIC), Programmable Logic Arrays (PLA), Field Programmable Gate Arrays (FPGA), special purpose electronic circuits, etc., or a combination thereof. The above first and second processing means may be separate processing means or they may be comprised in one processing means.
The term receiving means includes circuitry and/or devices suitable for enabling the communication of data, e.g. via a wired or a wireless data link. Examples of such receiving means include a network interface, a network card, a radio receiver, a receiver for other suitable electromagnetic signals, such as infrared light, e.g. via an IrDa port, radio-based communications, e.g. via Bluetooth transceivers, or the like. Further examples of such receiving means include a cable modem, a telephone modem, an Integrated Services Digital Network (ISDN) adapter, a Digital Subscriber Line (DSL) adapter, a satellite transceiver, an Ethernet adapter, or the like.
The term receiving means further comprises other input circuits/devices for receiving data signals, e.g. data signals stored on a computer-readable medium. Examples of such receiving means include a floppy-disk drive, a CD-Rom drive, a DVD drive, or any other suitable disc drive, a memory card adapter, a smart card adapter, etc.
The invention further relates to a data signal including multichannel signal information, the data signal being generated by a method described above and in the following. The signal may be embodied as a data signal on a carrier wave, e.g. as a data signal transmitted by communications means as described above and in the following.
The invention further relates to a computer-readable medium comprising a data record indicative of multichannel signal information generated by a method described above and in the following. The term computer-readable medium comprises magnetic tape, optical disc, digital video disk (DVD), compact disc (CD or CD-ROM), mini-disc, hard disk, floppy disk, ferro-electric memory, electrically erasable programmable read only memory (EEPROM), flash memory, EPROM, read only memory (ROM), static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), ferromagnetic memory, optical storage, charge coupled devices, smart cards, PCMCIA card, etc.
The invention further relates to a device for communicating a multichannel signal including at least a first signal component and a second signal component, the device comprising an arrangement for encoding the multichannel signal as described above and in the following.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments and with reference to the drawing, in which:
The coding device 101 comprises an encoder 102 for encoding a stereophonic signal according to the invention, the stereophonic signal including an L signal component and an R signal component. The encoder receives the L and R signal components and generates a coded signal T. The stereophonic signal L and R, may originate from a set of microphones, e.g. via further electronic equipment, such as a mixing equipment, etc. The signals may further be received as an output from another stereo player, over-the-air as a radio signal, or by any other suitable means. Preferred embodiments of such an encoder according to the invention will be described below. According to one embodiment, the encoder 102 is connected to a transmitter 103 for transmitting the coded signal T via a communications channel 109 to the decoding device 105. The transmitter 103 may comprise circuitry suitable for enabling the communication of data, e.g. via a wired or a wireless data link 109. Examples of such a transmitter include a network interface, a network card, a radio transmitter, a transmitter for other suitable electromagnetic signals, such as an LED for transmitting infrared light, e.g. via an IrDa port, radio-based communications, e.g. via a Bluetooth transceiver, or the like. Further examples of suitable transmitters include a cable modem, a telephone modem, an Integrated Services Digital Network (ISDN) adapter, a Digital Subscriber Line (DSL) adapter, a satellite transceiver, an Ethernet adapter, or the like. Correspondingly, the communications channel 109 may be any suitable wired or wireless data link, for example of a packet-based communications network, such as the Internet or another TCP/IP network, a short-range communications link, such as an infrared link, a Bluetooth connection or another radio-based link. Further examples of the communications channel include computer networks and wireless telecommunications networks, such as a Cellular Digital Packet Data (CDPD) network, a Global System for Mobile (GSM) network, a Code Division Multiple Access (CDMA) network, a Time Division Multiple Access Network (TDMA), a General Packet Radio service (GPRS) network, a Third Generation network, such as a UMTS network, or the like. Alternatively or additionally, the coding device may comprise one or more other interfaces 104 for communicating the coded stereo signal T to the decoding device 105. Examples of such interfaces include a disc drive for storing data on a computer-readable medium 110, e.g. a floppy-disk drive, a read/write CD-ROM drive, a DVD-drive, etc. Other examples include a memory card slot a magnetic card reader/writer, an interface for accessing a smart card, etc. Correspondingly, the decoding device 105 comprises a corresponding receiver 108 for receiving the signal transmitted by the transmitter and/or another interface 106 for receiving the coded stereo signal communicated via the interface 104 and the computer-readable medium 110. The decoding device further comprises a decoder 107 which receives the received signal T and decodes it into corresponding stereo components L′ and R′. Preferred embodiments of such a decoder according to the invention will be described below. The decoded signals L′ and R′ may subsequently be fed into a stereo player for reproduction via a set of speakers, head-phones, or the like.
y=L cos α+R sin α=w L L+w R R
r=−L sin α+R cos α=−w R L+w L R, (1)
where wL=cos α and wR=sin α will be referred to as weighting factors.
According to the invention, the angle α is determined such that it corresponds to a direction of high signal variance. The direction of maximum signal variance, i.e. the principal component, may be estimated by a principal component analysis such that the rotated y component corresponds to the principal component signal which includes most of the signal energy, and r is a residual signal. Correspondingly, the arrangement of
Initially, the incoming stereo signals L and R are rectified and lowpass filtered, resulting in envelope signals p(k) of L and q(k) of R, respectively, where p(k) and q(k) are suitably sampled and the sample index is denoted k. Thus, the vector x(k)=(p(k), q(k)) denotes the incoming signal vector. Alternatively, the signals L and R may be used directly, i.e. without filtering, or other filtered versions of L and R may be used, e.g. highpass filtered signals L and R. In
The principal component may be determined by any suitable method known in the art. In a particularly advantageous embodiment, an iterative method utilising Oja's rule (see e.g. S. Haykin: “Neural Networks”, Prentice Hall, N.J., 1999) is used. According to this embodiment, the weight vector w is iteratively estimated according to the following equation
where w(k)=(wL(k), wR(k)) corresponds to the estimate at time k. The above iteration may, for example, be initiated with a set of small random weights w(0), or in any other suitable way. The above estimated weight vector may be used to calculate the rotated signal according to y(k)=wT(k)x(k). Alternatively, the iteration of eqn. (2) may be performed on a block basis, e.g. for a block of N samples, where N depends on the particular implementation, for example, N=512, 1024, 2048, etc. In this embodiment, the estimated weight vector w(N) for a block may be used in the transformation of all samples of that block according to y(k)=wT(N)x(k).
The factor μ in eqn. (2) corresponds to a time scale of the tracking algorithm. If μ=0, the weighting factors and, thus, the angle α, remain constant, while they change rapidly for large μ. As an example, for a block size of 2048 samples, μ may be selected of the order of 10−3 for a sampling rate of 44.1 kHz.
It is an advantage of the above iterative algorithm that it is linear, i.e. it does not require the calculation of any trigonometric functions, square roots or the like. It is a further advantage, that the above iteration yields a normalised weight vector w, as the term −μw(k-1)y(k-1) in eqn. (2) corresponds to a weight decay term penalising large weights while the term +μx(k-1) drives the weight vector in the direction of the principal component. It is further noted that in the present embodiment, since x(k) is the envelope signal, wL, wR∈[0,1], i.e. the weight vector w lies in the first quadrant in
Again referring to
The arrangement further comprises encoders 202 performing a proper encoding of the signals y and r, respectively. For example, the signals may be encoded according to MPEG, e.g. MPEG I layer 3 (MP3), according to sinusoidal coding (SSC), or audio coding schemes based on subband, parametric, or transform schemes, or any other suitable schemes or combination thereof. It is understood that the encoders 202 may be of the same type or of different types, e.g. one MP3 encoder and one SSC encoder, etc. The resulting coded signals ye and re, respectively, are fed into a combiner circuit 204 together with the angle information α. The combiner circuit 204 performs framing, bit-rate allocation, and lossless coding, resulting in a combined signal T to be communicated. In one embodiment, the angle α or, alternatively, wL and/or wR may be communicated as part of a header transmitted prior to a signal frame, a signal block, or the like. According to the invention, as the transformation angle α is tracked such that the principal component signal includes most of the signal energy, the bit rates allocated to the y and r signals may be selected to be different, thereby optimising the coding efficiency.
For example, the stereo signals L and R may be expressed as L=M+S and R=M−S, where M corresponds to a mid or centre signal and S corresponds to a stereo or side signal. In the case of an acoustic recording of a stationary sound source, e.g. a speaker recorded by two microphones, the L and R signals are substantially equal, if the speaker is positioned exactly between the microphones and assuming that there are no acoustic distortions such as reflections, etc. Hence, in this case S is substantially zero or at least small and the coding scheme according to the invention substantially yields y corresponding to L+R and r corresponding to L−R being zero or small; this corresponds to α=45 degrees. If the speaker is not positioned exactly between the microphones, i.e. there is an asymmetry, but still assuming that there are no reflections or other distortions, the rotated signal y according to the invention still corresponds to the speaker and the residual signal r is substantially zero. However, in this case the angle α differs from 45 degrees. If the sound source moves, e.g. from left to right, the method according to the invention still yields a principal component signal y corresponding to the source and a small residual signal r, ideally being r=0. In this case, α changes form 0 (fully left) to 90 degrees (fully right).
The above example illustrates the advantage of tracking the angle α. In the above situations it may suffice to transmit the principal component signal y and the angle α, in order to allow the decoder to reconstruct the original signals R and L without a significant loss in quality. In general, as the residual signal r is small compared to the principal signal, the bit allocation or coding efficiency is tradable between y and r. Hence, it is an advantage of the invention that it allows an efficient coding of stereo signals.
Still referring to
In the embodiment described in connection with
In the example of
In the example of
In one embodiment, the reverberator 702 and the filter 701 may be fixed, i.e. not adapted according to the filter parameters Fp. Further, β2 may be fixed, thereby leaving the slowly varying parameter β1 as the only adaptive parameter which needs to be adjusted and transmitted. Consequently, a particularly simple filter arrangement is provided. It is an advantage of this embodiment that it only requires about half the original stereo bit rate for transmitting a stereo signal. It is noted that further variations of the above embodiment may be used. For example, in one embodiment the filter 701 may be left out.
Furthermore, alternatively or additionally to the correlation ρ, other measures of correlation may be used to ensure a high degree of similarity between the original signal and the signal after encoding-decoding. For example, in one embodiment two correlators may be used instead of correlator 705. One correlator may compute the cross-correlation ρLR of the input signals L and R. Furthermore, a second correlator may compute the cross correlation ρ′LR of the resulting outputs L′ and R′ of the encoder-decoder, i.e. according to this embodiment, the encoder further comprises a decoder circuit for determining the signals L′ and R′. This embodiment uses the difference ερ=ρLR−ρ′LR to control β2 such that ερ is minimal. This is illustrated in
It is understood that, according to one embodiment, only a subset of residual signals, e.g. r1, . . . , rk, k<n-1, maybe transmitted to the receiver or fed into corresponding filters, thereby reducing the necessary bit rate while maintaining most of the signal quality.
It is understood that a skilled person may adapt the above embodiments, e.g. by adding or removing features, or by combining features of the above embodiments. For example, it is understood that the features introduced in embodiments of
It is further noted that the invention is not limited to stereophonic signals, but may also be applied to other multi-channel input signals having two or more input channels. Examples of such multi-channel signals include signals received from a Digital Versatile Disc (DVD) or a Super Audio Compact Disc, etc. In this more general case, a principal component signal y and one or more residual signals r may still be generated according to the invention. The number of residual signals transmitted depends on the number of channels and the desired bit rate, as higher order residuals may be omitted without significantly degrading the signal quality.
In general, it is an advantage of the invention that bit-rate allocation may be adaptively varied, thereby allowing graceful degradation. For example, if the communication channel momentarily only allows a reduced bit rate to be transmitted, e.g. due to increased network traffic, noise, or the like, the bit rate of the transmitted signal may be reduced without significantly degrading the perceptible quality of the signal. For example, in the case of a stationary sound source discussed above, the bit rate may be reduced by a factor of approximately two without significantly degrading the signal quality, corresponding to transmitting a single channel instead of two.
It is noted that the above arrangements may be implemented as general- or special-purpose programmable microprocessors, Digital Signal Processors (DSP), Application Specific Integrated Circuits (ASIC), Programmable Logic Arrays (PLA), Field Programmable Gate Arrays (FPGA), special purpose electronic circuits, etc., or a combination thereof.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps than those listed in a claim. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
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|U.S. Classification||704/500, 704/E19.005, 381/23, 381/16, 704/504, 704/200.1, 381/19, 704/229, 381/22|
|International Classification||G10L19/008, H04B1/66, H04R5/00, H04H20/49, H03M7/30, H04H1/00|
|Cooperative Classification||G10L19/008, H04B1/667|
|European Classification||G10L19/008, H04B1/66S|
|Oct 5, 2004||AS||Assignment|
Owner name: KONINKLIJKE PHILIPS ELECTRONICS N.V., NETHERLANDS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:AARTS, RONALDUS MARIA;IRWAN, ROY;REEL/FRAME:016354/0219;SIGNING DATES FROM 20031003 TO 20031120
|Apr 10, 2012||FPAY||Fee payment|
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